<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>第60个CSS页面</title>
</head>
<body>

<div id="container" style="padding:50px; background-color:green; position:relative; width:200px; height:200px;">
    <div id="div1" style="width:100%; height:100%; border:2px solid blue;">
        <div id="content" style="border:1px solid red; position:absolute; left:0; top:0;">absolute element</div>
    </div>
</div>

</body>
</html>